1. Field of the Invention
The present invention relates to a linear motor driven elevator apparatus in which a car is moved using as a power source a linear induction motor.
2. Description of the Related Art
An example of this type of apparatus is the linear motor driven elevator disclosed in Japanese Patent Laid-Open No. Hei 1-271381. FIG. 7 is a schematic drawing showing an example of the arrangements of conventional linear motor driven elevators. In FIG. 7, reference numeral 1 denotes a car, reference numerals 2 and 3 denote pulleys, and reference numeral 4 denotes a rope for suspending the car 1 and a balance weight 4 through the pulleys 2 and 3 like a well bucket. Reference numeral 5 denotes an elevator passage wall, and reference numerals 6 and 7 denote secondary conductors, for example, made of aluminum (or copper), which are fixed to the elevator passage wall 5 so as to be opposed to each other. Reference numerals 6a and 7a denote joints of upper and lower secondary conductor members which form the secondary conductors 6 and 7, respectively. Reference numerals 8 and 9 each denote a primary winding of a linear induction motor loaded on the balance weight 10, and reference numeral 11 denotes the bottom of the elevator passage. The upper and lower secondary conductor members are connected to form a small gap at each of the joints 6a and 7a in consideration of the fact that a copper plate expands and contracts due to a temperature change in the environment where the elevator is installed, which is caused by a change in the season or the like.
FIG. 8 is an enlarged sectional view taken along line A--A in FIG. 7. In FIG. 8, reference numerals 8a, 8b and 9a, 9b denote the primary windings which are disposed on both sides of the respective secondary conductors opposite to each other with a predetermined gap therebetween to constitute a double-side linear induction motor.
In the linear motor-driven elevator arranged as described above, the car 1 is moved by the thrust generated by the interaction between an induced eddy current generated in each of the secondary conductors 6 and 7 and a shifting magnetic field generated at each of the gaps between the primary windings 8a and 8b and between the primary windings 9a and 9b. The shifting magnetic field is generated by exciting the primary windings 8 and 9 of the linear induction motor loaded on the balance weight 10, and the induced eddy current is generated by the shifting magnetic field. Namely, the balance weight 10 is driven by the relative thrust generated between the primary windings 8, 9 of the linear induction motor loaded on the balance 10 and the secondary conductors 6, 7. The thrust of the balance weight 10 is transmitted to the car 1 through the rope 4 so that the car 1 is upwardly and downward moved along a car rail (not shown) provided in the elevator passage. In this way, the elevator is operated.
In the conventional linear motor-driven elevator arranged as described above, the primary windings 8 and 9 of the linear induction motor loaded on the balance weight 10 are simultaneously passed through the joints 6a and 7a, respectively, of the secondary conductors 6 and 7, which are placed at a height h1 from the bottom 11 of the elevator passage. The thrust F is thus decreased by .DELTA.F1 with a center at the position h1 during passage through the joints, as shown in FIG. 9. This thrust change is generated due to the phenomenon that the eddy current I flowing through the secondary conductors 6 and 7 intermittently flows through the joints 6a and 7a, which phenomenon is caused by the presence of the gaps at the joints 6a and 7a of the secondary conductors 6 and 7, as shown in FIG. 10. The decrease .DELTA.F1 in the thrust causes the non-smooth movement of the car 1 each time the primary windings 8 and 9 pass through the joins 6a and 7a, respectively, thereby causing the problem of giving a jerking sensation to the passengers.